Fiber with elemental additive(s) and method of making

ABSTRACT

A multi-composition fiber is provided including a primary fiber material and an elemental additive material deposited on grain boundaries between adjacent crystalline domains of the primary fiber material. A method of making a multi-composition fiber is also provided, which includes providing a precursor laden environment, and promoting fiber growth using laser heating. The precursor laden environment includes a primary precursor material and an elemental precursor material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication Ser. No. 62/427,362, filed Nov. 29, 2016, entitled “Fiberwith Elemental Additives and Method of Making”, which is herebyincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates generally to the field of fibers forreinforcing materials and more specifically to the field of fibershaving elemental additives.

In a wide variety of applications, fiber composite materials,incorporating fibers into a surrounding material matrix, provide higherstructural performance than traditional, bulk (i.e.,non-fiber-reinforced) materials. Unfortunately, however,conventionally-produced, single-composition fibers often suffer frompoor creep resistance at elevated temperatures due to diffusion-drivengrain growth increasing the average grain size by, in some cases, morethan two orders of magnitude.

SUMMARY

As described herein, the above-noted grain growth process often proceedsby atomic diffusion through grain boundary paths, and therefore, theaddition of oversized atoms (i.e., one or more elemental additives) atgrain boundaries presents an energy barrier to atomic diffusion and thusincreases creep resistance by slowing down grain growth at elevatedtemperatures in the formed fiber. Opportunities exist, therefore, toimprove fiber creep resistance performance by providing amulti-composition fiber with elemental additives.

The opportunities described above are addressed, in one aspect of thepresent invention, by a multi-composition fiber comprising a primaryfiber material and an elemental additive material deposited on grainboundaries between adjacent crystalline domains of the primary fibermaterial. In another aspect of the present invention, a method of makinga multi-composition fiber is provided, which comprises providing aprecursor laden environment and promoting fiber growth using laserheating, the precursor laden environment comprising a primary precursormaterial and an elemental precursor material.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, andwherein:

FIG. 1 is a schematic representation of a single-fiber reactor, showinga seed fiber substrate, a reactor cube into which precursor gases aredelivered, a focused laser beam impinging on the seed fiber, and reactorwindows that are transparent to the incoming laser beam wavelength andallow for, for instance, video monitoring of the process, in accordancewith one or more aspects of the present invention;

FIG. 2 is a schematic view showing how LCVD can be massivelyparallelized by a multiplication of the laser beams, in accordance withone or more aspects of the present invention;

FIG. 3 depicts an example of parallel LCVD growth of carbon fibers, inaccordance with one or more aspects of the present invention;

FIG. 4A is a simplified schematic of components of an LCVD systemfacilitating fabrication of a multi-composition fiber with elementaladditive(s), in accordance with one or more aspects of the presentinvention;

FIG. 4B depicts one embodiment of a process for fabricating amulti-composition fiber with elemental additive(s), in accordance withone or more aspects of the present invention;

FIG. 5 depicts a partial embodiment of a multi-composition fiber withelemental additive(s), in accordance with one or more aspects of thepresent invention;

FIG. 6A is a partial cross-sectional view of a multi-composition fiberwith elemental additive(s) at the grain boundaries, in accordance withone or more aspects of the present invention; and

FIG. 6B graphically depicts impact on creep resistance with the additionof secondary elemental material at the grain boundary structures of amulti-composition fiber, in accordance with one or more aspects of thepresent invention.

DETAILED DESCRIPTION

Aspects of the present invention and certain features, advantages anddetails thereof, are explained more fully below with reference to thenon-limiting example(s) illustrated in the accompanying drawings.Descriptions of well-known systems, devices, fabrication and processingtechniques, etc., are omitted so as to not unnecessarily obscure theinvention in detail. It should be understood, however, that the detaileddescription and the specific example(s), while indicating aspects of theinvention, are given by way of illustration only, and are not by way oflimitation. Various substitutions, modifications, additions, and/orarrangements, within the spirit and/or scope of the underlying inventiveconcepts will be apparent to those skilled in the art from thisdisclosure. Note further that numerous inventive aspects and featuresare disclosed herein, and unless inconsistent, each disclosed aspect orfeature is combinable with any other disclosed aspect or feature asdesired for a particular application, for instance, for facilitatingproviding multi-composition fibers with elemental additive(s) andmethods of making, as described herein.

Before describing the above-noted aspects further, note that the presentinvention incorporates or utilizes the following, alone or in anycombination, and/or in combination with the subject matter of commonlyassigned, International Patent Application No. PCT/US2015/037080, whichpublished on Dec. 30, 2015, as PCT Patent Publication No. WO 2015/200257A1, and with commonly assigned, U.S. patent application Ser. No.15/114,504, filed Jul. 27, 2016, entitled: Contiguously BlendedNano-Scaled Multi-Phase Fibers”, which published on Dec. 1, 2016, asU.S. Patent Publication No. 2016/0347672 A1, and with commonly assigned,U.S. patent application Ser. No. 15/320,800, filed Dec. 21, 2016,entitled “An Additive Manufacturing Technology for the Fabrication andCharacterization of Nuclear Reactor Fuel”, which published on Jul. 27,2017, as U.S. Patent Publication No. 2017/0213604 A1, and with commonlyassigned, U.S. patent application Ser. No. 15/592,408, filed May 11,2017, entitled “Fiber Delivery Assembly and Method of Making”, and withcommonly assigned, U.S. patent application Ser. No. 15/592,726, filedMay 11, 2017, entitled “Multilayer Functional Fiber and Method ofMaking”, and with commonly assigned, U.S. patent application Ser. No.15/631,243, filed Jun. 23, 2017, entitled “Nanofiber-Coated Fiber andMethods of Making”, and with commonly assigned, U.S. patent applicationSer. No. 15/718,199, filed Sep. 28, 2017, entitled “Multi-CompositionFiber with Refractory Additive(s) and Method of Making”, and withcommonly assigned U.S. patent application Ser. No. 15/718,206, filedSep. 28, 2017, entitled “Refractory Oxide Coated Fiber and Method ofMaking”, each of which is hereby incorporated herein by reference in itsentirety.

Fiber-reinforced composite materials are designed to concomitantlymaximize strength and minimize weight. This is achieved by embeddinghigh-strength low-density fibers into a low-density filler matrix insuch a way that fibers channel and carry the structural stresses incomposite structures. The matrix serves as a glue that holds fiberstogether and helps transfer loads in shear from fiber to fiber, but infact the matrix material is not a structural element and carries but afraction of the overall structural load seen by a composite material.

Composites are thus engineered materials made up of a network ofreinforcing fibers—sometimes woven, knitted or braided—held together bya matrix. Fibers are usually packaged as twisted multifilament yarnscalled “tows”. The matrix gives rise to three self-explanatory classesof composite materials: (1) Polymer Matrix Composites (PMCs),sometimes-called Organic Matrix Composites (OMCs); (2) Metal MatrixComposites (MMC's); and (3) Ceramic Matrix Composites (CMCs).

Such an approach to composite materials in which the tows are but adisorganized bundle of entangled filaments constrains the fibers to apurely structural role. A new approach to the fabrication ofmultilayered fibers called 1½-D printing allows for the formation ofevenly spaced, parallel filaments. Together, this construct constitutesan arbitrary long ribbon of continuous filaments that allow the fiber tobreak out of their purely structural functions, and enable sweeping newdesigns in which the fibers contain embedded microsystems. This isdescribed further in the above-referenced, commonly assigned, U.S.patent application Ser. No. 15/592,408.

This approach to fiber manufacturing has been proposed for example as ameans to produce TRISO-inspired nuclear fuel embedded within fibers forsubsequent embedding into a refractory matrix to form an accidenttolerant CMC nuclear fuel, such as described in the above-referenced,commonly assigned PCT Patent Publication No. WO 2015/200257 A1. However,this is but one instance of possible new designs enabled by thistechnology.

At its core, 1½-D printing rests on the physical principles of LaserInduced Chemical Vapor Deposition to both print continuous filaments anddeposit patterns coated onto the fiber. Commonly assigned, U.S. patentapplication Ser. No. 14/372,085, filed Jul. 14, 2014, entitled “HighStrength Ceramic Fibers and Methods of Fabrication”, which published onJan. 1, 2015, as U.S. Patent Publication No. 2015/0004393 A1, teacheshow arrays of filaments can be laser-printed, with diameters potentiallyvarying along their length. The above-referenced, PCT Patent PublicationNo. WO 2015/200257 A1 teaches how a laser incident to the ribbon can beused to write a pattern of coatings onto a substrate fiber by turningthe laser on or off as the ribbon advances. It also teaches that coatingthickness can be adjusted. Finally, the above-referenced, commonlyassigned U.S. patent application Ser. No. 15/592,408, teaches how suchribbons of parallel filaments can be collected as ribbons onto a tape toenhance fiber volume fraction in the composite.

To implement 1½-D printing, Laser Induced Chemical Vapor Deposition(LCVD) was chosen as the fundamental Additive Manufacturing (AM) toolfor its near material independence—an extremely rare property for AMprocesses. Such a process is said to be “Material Agnostic”. LCVD is atechnique derived from CVD, used intensively in the microelectronicsfabrication industry (aka “Chip Fab”). CVD builds up electronics-gradehigh-purity solid deposits from a gas precursor. In its 75+ yearhistory, Chip Fab has accumulated an impressive library of chemicalprecursors for a wide range of materials, numbering in the 10's ofthousands. The main difference between CVD and LCVD resides indimensionality and mass throughput. CVD is intended for 2-D film growthwhereas LCVD is ideally suited for one-dimensional filamentarystructures. The dimensionality difference means that depositionmechanisms are greatly enhanced for LCVD vs. CVD, leading to depositedmass fluxes (kg/m2 s) that are 3 to 9 orders of magnitude greater. Forexample, diamond-like carbon filaments have been measured at lineargrowth rates upwards of 13 cm/s, which represents a 9 order of magnitudeincrease in mass flux compared to thin film CVD of the same material.Finally, LCVD is essentially containerless, which virtually eliminatesopportunities for material contamination by container or tool.

The following fundamental properties formally defines “1½-D Printing” AM

-   -   Material-agnostic ability to grow filaments.    -   Ability to vary diameter along the length of the filament, as        illustrated in FIG. 10 of Pegna et al. (PCT Publication No. WO        2015/200257 A1).    -   Material-agnostic ability to vary composition along the length        of the filament, as was demonstrated by Maxwell et al.    -   Material-agnostic ability to coat specific sections of filaments        with a desired material, morphology and thickness; as        illustrated by the nanoporous and other spot coatings shown in        FIG. 11 of the above-referenced Pegna et al., PCT publication.

Disclosed herein, in part, is the concept of avoiding the use ofpolymeric precursors altogether by using laser-assisted chemical vapordeposition (LCVD) as is described in U.S. Pat. No. 5,786,023, entitled“Method and Apparatus for the Freeform Growth of Three-DimensionalStructures Using Pressurized Precursor Flows and Growth Rate Control”,by Maxwell and Pegna, the entirety of which is hereby incorporated byreference herein. In this process pure precursor gases (such as silaneand ethylene in the case of SiC fiber production) are introduced into areactor within which a suitable substrate such as glassy carbon ispositioned, and laser light is focused onto the substrate. The heatgenerated by the focused laser beam breaks down the precursor gaseslocally, and the atomic species deposit onto the substrate surface andbuild up locally to form a fiber. If either the laser or the substrateis pulled away from this growth zone at the growth rate a continuousfiber filament will be produced with the very high purity of thestarting gases. With this technique there are virtually no unwantedimpurities, and in particular no performance-robbing oxygen.

Very pure fibers can be produced using LCVD, such as silicon carbide,boron carbide, silicon nitride and others. The inventors have discoveredthat if a material has been deposited using CVD, there is a good chancethat fiber can be produced using LCVD. Unlike with liquid polymericprecursors, however, where the chemistry can be very involved andcomplicated even for relatively ‘simple’ materials such as thosementioned above, LCVD can also be used quite directly to produce novelmixes of solid phases of different materials that either cannot be madeor have not been attempted using polymeric precursor and spinnerettechnology. Examples include fibers composed of silicon, carbon andnitrogen contributed by the precursor gases such as silane, ethylene andammonia, respectively, where the resulting “composite” fiber containstightly integrated phases of silicon carbide, silicon nitride andsilicon carbonitrides depending on the relative concentrations ofprecursor gases in the reactor. Such new and unique fibers can exhibitvery useful properties such as high temperature resistance, highstrength and good creep resistance at low relative cost.

FIG. 1 shows a LCVD reactor into which a substrate seed fiber has beenintroduced, onto the tip of which a laser beam is focused. (It will beseen that the substrate may be any solid surface capable of being heatedby the laser beam. It will further be seen that multiple lasers could beused simultaneously to produce multiple simultaneous fibers as is taughtin International Patent Application Serial No. PCT/US2013/022053, whichpublished on Dec. 5, 2013, as PCT Patent Publication No. WO 2013/180764A1, and in U.S. Patent Publication No. 2015/0004393, the entireties ofwhich are hereby incorporated by reference herein. In accordance withthat Application, FIG. 1 more particularly shows a reactor 10; enlargedcutout view of reactor chamber 20; enlarged view of growth region 30. Aself-seeded fiber 50 grows towards an oncoming coaxial laser 60 and isextracted through an extrusion microtube 40.

A mixture of precursor gases can be introduced at a desired relativepartial pressure ratio and total pressure. The laser is turned on,generating a hot spot on the substrate, causing local precursorbreakdown and local CVD growth in the direction of the temperaturegradient, typically along the axis of the laser beam. Material willdeposit and a fiber will grow, and if the fiber is withdrawn at thegrowth rate, the hot spot will remain largely stationary and the processcan continue indefinitely, resulting in an arbitrarily long CVD-producedfiber.

Also in accordance with that Application, a large array of independentlycontrolled lasers can be provided, growing an equally large array offibers 70 in parallel, as illustrated in FIG. 2, showing how fiber LCVDcan be massively parallelized from a filament lattice 100 bymultiplication of the laser beams 80 inducing a plasma 90 around the tipof each fiber 70. Using a Computer to Plate (CtP) (e.g., Quantum WellIntermixing (QWI)) laser array for LCVD is a scientific first, and sowas the use of a shallow depth of focus. It provides very beneficialresults. Sample carbon fibers, such as those shown in FIG. 3, were grownin parallel. FIG. 3 shows parallel LCVD growth of carbon fibers—Left:Fibers during growth and Right: Resulting free standing fibers 10-12 μmin diameter and about 5 mm long.

As discussed herein, laser-driven, chemical-vapor deposition (LCVD)technology is capable of forming high-performance ceramic and inorganicfibers for composite material systems. FIG. 1 discussed above is aschematic representation of a monofilament LCVD production process. FIG.4A is a simplified view of an LCVD production system for producing amulti-composition fiber with one or more elemental additives, inaccordance with one or more aspects of the present invention, and FIG.4B depicts an exemplary process for producing a multi-composition fiberwith one or more elemental additives, in accordance with one or moreaspects of the present invention.

Referring to FIG. 4A, the LCVD system 400 shown includes a chamber 401into which one or more lasers 402 are directed through one or morewindows 403. Chamber 401 includes precursor gases 404 for facilitatingproducing a fiber 405 such as disclosed herein. A fiber extractionapparatus 406 facilitates withdrawing the fiber as it is produced withinthe chamber.

The deposition process may include bringing precursor gases into thechamber 410, as illustrated in FIG. 4B. For a given fabrication process,ratios of the precursor gases are selected and introduced into thechamber. The gases contain the atomic species that are to be depositedin the fiber format. For instance, silicon carbide fibers (SiC) may beformed from silicon-containing and carbon-containing gases, or a singlegas that contains both atoms. In addition, a small laser beam isdirected into the gas-containing chamber through a window that transmitsthe laser wavelength 412. This laser beam is focused onto an initiationsite, which can be a fiber seed, a thin substrate, or any other solidcomponent that will heat up upon being intersected by the beam andabsorb its energy. At this hot spot 414, the precursor gasesdisassociate and, through certain chemical reaction steps, deposit adesired solid product. For instance, in the example above, the solid SiCdeposit accreting together form the fiber 416. The fiber itself growstowards the laser source, and thus the fiber is pulled away and out ofthe reactor at an equivalent fiber growth rate 418. In this manner, thedeposition zone remains at a constant physical position (the focal pointof the laser beam), and deposition can continue indefinitely, as long asthe laser beam is on and the supply of precursor gases is replenished.

As noted above, FIG. 2 provides a representation of a massiveparallelization of the laser beam input, increased from a single beam toa multitude of individually controlled laser beams, to producehigh-quality volume array of parallel fibers.

By control of the localized chemistry formed in LCVD-produced fibers,multiple materials may be deposited simultaneously and homogeneouslythroughout the fiber microstructure. This approach can produce aninorganic, multiple material composite fiber by the LCVD process, whichis composed of several desired chemistries. The localized chemistry isdriven through controlled composition of the gas precursor feed. Theaddition of elemental atoms to the grain boundaries between the formedcrystallites may require the gas precursor for that desired element tobe less than approximately 5% atomic of the overall input gascomposition.

In accordance with one embodiment of the present invention, FIG. 5illustrates a high-level depiction of a multi-composition fiber 500comprising a primary fiber material 540 and an elemental additivematerial 550 deposited on grain boundaries between adjacent crystallinedomains of primary fiber material 540.

In a more detailed embodiment, primary fiber material 540 is arefractory-grade, inorganic primary fiber material, which may include,but not be limited to, compositions such as silicon carbide, boroncarbide, silicon nitride, zirconium carbide, hafnium diboride, hafniumcarbide, tantalum carbide, niobium carbide, tantalum diboride, zirconiumdiboride, tungsten diboride, hafnium nitride, tantalum nitride,zirconium nitride, and combinations thereof.

In another more detailed embodiment, elemental additive material 550 isselected from a group consisting of hafnium, tantalum, niobium, yttrium,lanthanum, cerium, zirconium, molybdenum, tungsten, and combinationsthereof.

In another more detailed embodiment, multi-composition fiber 500 has asubstantially non-uniform diameter. For instance, user-directed inputsfor the LCVD process growth parameters, such as input laser power andprecursor gas characteristics, provide exquisite control over the finalformed fiber chemical and physical properties. For instance, thesegrowth parameters can be altered to impart variations in the fiberdiameter dimension. In effect, the fiber diameter may be changed from athinner-to-thicker-to-thinner section (or vice versa), which can berepeated in a desired periodicity or designed in some manner to impartdesired physical properties for the fibers in the overall compositeperformance.

In another aspect of the present invention, a method of making amulti-composition fiber 500 comprises providing a precursor ladenenvironment 510 and promoting fiber growth using laser heating.Precursor laden environment 510 comprises a primary precursor material520 and an elemental precursor material 530.

In a more detailed embodiment, primary precursor material 520 comprisesa precursor for a material selected from a group which may include, butnot be limited to, compositions such as silicon carbide, boron carbide,silicon nitride, zirconium carbide, hafnium diboride, hafnium carbide,tantalum carbide, niobium carbide, tantalum diboride, zirconiumdiboride, tungsten diboride, hafnium nitride, tantalum nitride,zirconium nitride, and combinations thereof.

In another more detailed embodiment, elemental precursor material 550comprises a precursor for a material selected from a group consisting ofhafnium, tantalum, niobium, yttrium, lanthanum, cerium, zirconium,molybdenum, tungsten, and combinations thereof.

In another more detailed embodiment, precursor laden environment 510comprises a material selected from a group consisting of gases, liquids,critical fluids, supercritical fluids, and combinations thereof.

In another alternative embodiment, the act of promoting fiber growthusing laser heating comprises modulating the laser heating such that themulti-composition fiber 500 has a substantially non-uniform diameter.

By way of further example, FIG. 6A shows an LCVD formed fiber, such asfiber 500 of FIG. 5, with preferential deposition of the desiredelemental atoms 620 (FIG. 6A) at grain boundary locations 610 betweenthe grains 600 of the primary fiber material. Advantageously, theelemental material is too large to fit within the grains themselves, forinstance, within the crystalline structure of the grains, and thus,resides at the boundaries of the grains, as illustrated.

FIG. 6B depicts the schematic relationship of the impact on creepresistance by the addition of elemental material, i.e., secondaryelements, to the grain boundary structure of an inorganic materialthrough the change in grain size versus exposure time at elevatedtemperatures (e.g., above 800° C.) as compared to an inorganic materialthat has no secondary element material additions at the grainboundaries.

Those skilled in the art will note from the above description thatprovided herein are multi-composition fibers and methods of fabrication.For instance, the multi-composition fiber may include a primary fibermaterial and an elemental additive material disposed on grain boundariesbetween adjacent crystalline domains of the primary fiber material. Inone or more embodiments, the primary fiber material is arefractory-grade, inorganic primary fiber material. For instance, theprimary fiber material may be a silicon carbide, boron carbide, siliconnitride, zirconium carbide, hafnium diboride, hafnium carbide, tantalumcarbide, niobium carbide, tantalum diboride, zirconium diboride,tungsten diboride, hafnium nitride, tantalum nitride, zirconium nitride,and combinations thereof. In one or more embodiments, the elementaladditive material may be hafnium, tantalum, niobium, yttrium, lanthanum,cerium, zirconium, molybdenum, tungsten, and combinations thereof.Further, the multi-composition fiber may have a uniform, or anon-uniform, diameter. That is, in one or more implementations, thediameter of the multi-composition fiber may vary, as desired for aparticular application.

In one or more implementations, the multi-composition fiber may includea primary fiber material and an elemental additive material deposited ongrain boundaries between adjacent crystalline domains of the primaryfiber material, where the primary fiber material is or includes one ormore of: silicon carbide, boron carbide, silicon nitride, zirconiumcarbide, hafnium diboride, hafnium carbide, tantalum carbide, niobiumcarbide, tantalum diboride, zirconium diboride, tungsten diboride,hafnium nitride, tantalum nitride, zirconium nitride, and/orcombinations thereof, and the elemental additive material is one or moreof hafnium, tantalum, niobium, yttrium, lanthanum, cerium, zirconium,molybdenum, tungsten, and/or combinations thereof. Further, themulti-composition fiber may have a uniform, or a substantiallynon-uniform diameter, as desired.

In one or more aspects, a method of making a multi-composition fiber isprovided herein. The method includes providing a precursor ladenenvironment; promoting fiber growth using laser heating; and wherein theprecursor laden environment includes a primary precursor material and anelemental precursor material. In one or more implementations, theprimary fiber material is a refractory-grade, inorganic primary fibermaterial. For instance, the primary fiber material may include aprecursor for a material selected from a group consisting of: siliconcarbide, boron carbide, silicon nitride, zirconium carbide, hafniumdiboride, hafnium carbide, tantalum carbide, niobium carbide, tantalumdiboride, zirconium diboride, tungsten diboride, hafnium nitride,tantalum nitride, zirconium nitride, and/or combinations thereof. In oneor more embodiments, the elemental precursor material may be a precursorfor material selected from a group consisting of: hafnium, tantalum,niobium, yttrium, lanthanum, cerium, zirconium, molybdenum, tungsten,hafnium carbide, tantalum carbide, niobium carbide, tantalum diboride,zirconium diboride, tungsten diboride, hafnium nitride, tantalumnitride, zirconium nitride, and/or combinations thereof. In one or moreimplementations, the precursor laden environment may include a materialselected from a group consisting of: gases, liquids, critical fluids,super-critical fluids, and combinations thereof. Further, promotingfiber growth using laser heating may include modulating the laserheating such that the multi-composition fiber has a substantiallynon-uniform diameter.

In one or more embodiments, disclosed herein is a method of making amulti-composition fiber which includes: providing a precursor ladenenvironment, promoting fiber growth using laser heating; and wherein theprecursor laden environment includes a primary precursor material and anelemental precursor material. The primary precursor material includes aprecursor for a material selected from a group consisting of: siliconcarbide, boron carbide, silicon nitride, zirconium carbide, hafniumdiboride, hafnium carbide, tantalum carbide, niobium carbide, tantalumdiboride, zirconium diboride, tungsten diboride, hafnium nitride,tantalum nitride, zirconium nitride, and/or combinations thereof. Theelemental precursor material includes a precursor for a materialselected from a group consisting of: hafnium, tantalum, niobium,yttrium, lanthanum, cerium, zirconium, molybdenum, tungsten, and/orcombinations thereof. In one or more embodiments, the precursor ladenenvironment includes a material selected from a group consisting ofgases, liquids, critical fluids, super-critical fluids, and combinationsthereof. Further, promoting fiber growth using laser heating may includemodulating the laser heating such that the multi-composition fiber has asubstantially non-uniform diameter along its length.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of one or more aspects of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand one or more aspects of the invention for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A multi-composition fiber comprising a primaryfiber material and an elemental additive material deposited on grainboundaries between adjacent crystalline domains of the primary fibermaterial.
 2. The multi-composition fiber of claim 1, wherein the primaryfiber material is a refractory-grade, inorganic primary fiber material.3. The multi-composition fiber of claim 1, wherein the primary fibermaterial is selected from a group consisting of silicon carbide, boroncarbide, silicon nitride, zirconium carbide, hafnium diboride, hafniumcarbide, tantalum carbide, niobium carbide, tantalum diboride, zirconiumdiboride, tungsten diboride, hafnium nitride, tantalum nitride,zirconium nitride, and combinations thereof.
 4. The multi-compositionfiber of claim 1, wherein the elemental additive material is selectedfrom a group consisting of hafnium, tantalum, niobium, yttrium,lanthanum, cerium, zirconium, molybdenum, tungsten, and combinationsthereof.
 5. The multi-composition fiber of claim 1, wherein themulti-composition fiber has a substantially non-uniform diameter.
 6. Amulti-composition fiber comprising a primary fiber material and anelemental additive material deposited on grain boundaries betweenadjacent crystalline domains of the primary fiber material: the primaryfiber material being selected from a group consisting of siliconcarbide, boron carbide, silicon nitride, zirconium carbide, hafniumdiboride, hafnium carbide, tantalum carbide, niobium carbide, tantalumdiboride, zirconium diboride, tungsten diboride, hafnium nitride,tantalum nitride, zirconium nitride, and combinations thereof: and theelemental additive material being selected from a group consisting ofhafnium, tantalum, niobium, yttrium, lanthanum, cerium, zirconium,molybdenum, tungsten, and combinations thereof.
 7. The multi-compositionfiber of claim 6, wherein the multi-composition fiber has asubstantially non-uniform diameter.
 8. A method of making amulti-composition fiber, the method comprising: providing a precursorladen environment; promoting fiber growth using laser heating; andwherein the precursor laden environment comprises a primary precursormaterial and an elemental precursor material.
 9. The method of claim 8,wherein the primary fiber material is a refractory-grade, inorganicprimary fiber material.
 10. The method of claim 8, wherein the primaryprecursor material comprises a precursor for a material selected from agroup consisting of silicon carbide, boron carbide, silicon nitride,zirconium carbide, hafnium diboride, hafnium carbide, tantalum carbide,niobium carbide, tantalum diboride, zirconium diboride, tungstendiboride, hafnium nitride, tantalum nitride, zirconium nitride, andcombinations thereof.
 11. The method of claim 8, wherein the elementalprecursor material comprises a precursor for a material selected from agroup consisting of hafnium, tantalum, niobium, yttrium, lanthanum,cerium, zirconium, molybdenum, tungsten, and combinations thereof. 12.The method of claim 8, wherein the precursor laden environment comprisesa material selected from a group consisting of gases, liquids, criticalfluids, supercritical fluids, and combinations thereof.
 13. The methodof claim 8, wherein the promoting fiber growth using laser heatingcomprises modulating the laser heating such that the multi-compositionfiber has a substantially non-uniform diameter.
 14. A method of making amulti-composition fiber, the method comprising: providing a precursorladen environment; promoting fiber growth using laser heating; andwherein the precursor laden environment comprises a primary precursormaterial and an elemental precursor material: the primary precursormaterial comprising a precursor for a material selected from a groupconsisting of silicon carbide, boron carbide, silicon nitride, zirconiumcarbide, hafnium diboride, hafnium carbide, tantalum carbide, niobiumcarbide, tantalum diboride, zirconium diboride, tungsten diboride,hafnium nitride, tantalum nitride, zirconium nitride, and combinationsthereof; and the elemental precursor material comprising a precursor fora material selected from a group consisting of hafnium, tantalum,niobium, yttrium, lanthanum, cerium, zirconium, molybdenum, tungsten,hafnium carbide, tantalum carbide, niobium carbide, tantalum diboride,zirconium diboride, tungsten diboride, hafnium nitride, tantalumnitride, zirconium nitride, and combinations thereof.
 15. The method ofclaim 14, wherein the precursor laden environment comprises a materialselected from a group consisting of gases, liquids, critical fluids,supercritical fluids, and combinations thereof.
 16. The method of claim14, wherein the promoting fiber growth using laser heating comprisesmodulating the laser heating such that the multi-composition fiber has asubstantially non-uniform diameter.